1. Field of the Invention
This invention relates to semiconductor integrated microcircuit manufacturing and more particularly to temporarily packaging singulated integrated circuit dice for shipping.
2. State of the Art
Semiconductor integrated circuit chips are typically constructed en masse on a single wafer or other substrate of silicon or other semiconductor material. After the circuits are created, the wafers or substrates are split up, or "singulated", into individual integrated circuit chips or dice. Typically, each die is then individually encapsulated into integrated circuit packages which are capable of being attached to printed circuit boards. However, dice are often sold or transferred to other manufacturing sites in the unpackaged form. The unpackaged dice must therefore be shipped through the mail or by other freight means to destinations which can be cities, states or even countries apart. Freight travel often involves subjecting articles so transported to a harsh, contaminant-laden environment in terms of dirt and dust, as well as mechanical shock and vibration. This environment requires that the dice be temporarily packaged to protect them from such exposure.
Over the years, the industry has developed packages called die-pacs which temporarily contain the dice during shipping. Currently, die-pacs are protective containers similar to that shown in FIG. 1. The containers are made of black conductive polypropylene to keep out dust and other contaminants and to protect the die from static charges and from crushing and impact type forces caused by rough handling. The container comprises a lower bed structure 1 which is capable of being mated to a cover structure 2. When mated, an inner cavity 3 is formed for storing the die 4 or dice. The bed and cover are held together through temporary securing means such as interlocking clasp brackets 5 and 6. The position of the die within the cavity of the container is secured by a layer of silicone gel adhesive material 7 contacting the undersurface of the die and a surface of the bed facing the inner cavity.
The silicone gel is similar to common household cellophane wrapping material. However, silicone gel has greater resiliency and will not hold a static electric charge of any significance.
Prior to shipping, the singulated dice are placed atop the silicone gel layer on the bed through robot deposit or other means. The cover is then mated and secured to the bed using the interlocking clasp brackets. The die-pac is then ready for shipment.
Upon arrival of the die-pac at its destination, the interlocking clasp brackets are removed and the cover lifted from the bed. Robot-operated pickup means then remove the die or dice from the bed.
There are, however, certain problems which have arisen using the popular silicone gel die-pac. First, the adhesive nature of the silicone gel, which is strong enough to maintain the position of the die during transport, requires either expensive manual removal of the dice or that the robot pickup means be sufficiently strong to remove the die from the gel. This relatively powerful pickup means sometimes can damage the sensitive die during the pickup operation. When less strong means are used, there are often many unsuccessful attempts made before the die is picked-up. Repetitive attempts to pick-up a die increases the probability of damaging the die during the pick-up process.
Second, it has been found that residue from the silicone gel often contaminates portions of the die. This residue is in the form of silicon compounds such as silicon oxides and silicon-metal compounds. Tests have shown particularly high concentrations of compounds such as polydimethylsiloxane (CH.sub.3 --(Si--O).sub.n --CH.sub.3). These compounds generally contaminate the surfaces of a die, resulting most commonly in reduced conductivity of the die's electrical contact points, thereby forcing further costly processing prior to packaging. Severe contamination will even cause a die to be non-functional.
Therefore, it would be valuable to have a method for shipping singulated dice which does not subject the dice to the problems associated with the prior art packaging techniques as referenced above.